Color television receiver



May 17, 1960 c. H. JoNr-:s

coLoR TELEvIsIoN RECEIVER Filed March 17. 1954 m nm...-

COLOR TELEVISION RECEIVER Charles H. Jones, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a

corporation of Pennsylvania Application March 17, 1954, serial No. 416,916

z claims. (cl.- 178-524) My invention relates to`c'o1or'television receivers and in particular relates to an improved type of receiver for, the signals of the color television systemrecomme'nded.; for standardization by the National Color Television'Y Systems Committee (hereinafter referred to as the NTSC system) which is described in the NTSC Color Field Specifications submitted tothe Federal Communications Commission in 1953. A description of this vsystem believed tobe suiciently detailedlfor present purposes is contained inan article Principles of NTSC National Television by Hirsch et al. in the February 1952 number of Electronics published by McGraw-Hill Publishing Company, New York City.

In the above-mentioned 'NTSC standardization color system advantage is taken of the eXperimentally-estab-- lished fact that the human eye is much less sensitive to" tine gradations in intensity of color in pictures than it is v to fine gradations of total luminous intensity by transmitting a carrier which is modulated with all frequencies of variation` from thirty cycles to four megacyclesfin the' totaliluminosity' (regardless ofcolr) of the'picture being sent, and a subcarrier which is modulated by those color" variations which occur at frequencies up to about one megacycle.

At the receiver the above-mentionedV carrier and sub-v carrier. are detectedin conventional RF, IF and second detector ra'dio receiver circuits, and the picture-signals demodulated then for application to a color kinescope. A

number of diffe/rent Ways of effecting this demodulation tively cophasal with the incoming subcarrier, dephased" 2,937,231 luolteril:ed May 17, l1960 ,ICC

quantity of about .2 or' 2.2 in value which will be explained later.` We willsimilarly refer to the high frequency portion of the Y' signal kcontaining frequencies from 1 to 3.5

mc. as Y'h In thejsystems described in the Electronics article the three signals described in the preceding paragraph are each added to the full frequency-signal Y to produce three outputs 1 1 1 -K2(G.7 if Yin); KKR? 'i- Y'h) and K4 B7 *i* Y'h) which are'respectively impressed on three control electrodes for scanning beams which generate green, red and blue ylight fromfluorescent screen elements they are incidentupo'n. 4

The light emission L from phosphors is found to be proportional-to the'power 'y of the voltage impressed on the grid which controls the scanning beam intensity so the light-colors seen by one observing the picture screen are respectively When there are no picture-intensity iiuctuations of frequencyV greater than one megacycle Yh=0 and L=G,

L=R and L=B.; thus the picture screen gives a true rendition of the/color information transmitted to it; but when "the `v'colorffvariations Voffr'equency above one megacycle by |90 from it, and dephased by 44235.59 from it. A

sync .burst for thesubcarrier synchronization is transmitted during each horizontal retrace interval. Y

-As described in the above-mentioned YElectronics article, the output vof the second detector divides into two channels, one of which passes a band of frequencies be-l other of which passes a band between 2.5 and 4.0 mega-- cycles and so includes the subcarrier which is Aof approxi?.

mately 3.58megacycles, and the band of its color modu-y lators. `By combining the content of this second channel iur-'the `respectivefcolors as. to which no information is embodied in the transmitted signal, bear the same intensity-ratios to each other as do the color variations of frequency below one megacycle. This may be accomplished by the circuit described below.

'.One'object'fof my invention is accordingly toprovid an'improved color television receiver.

YAnother objectof my invention is to provide an iin-- provedrecewer for color television signals in whichmodulationsiof a main carrier Wave conveys information as to picture luminosity variations of substantially all frequencies while modulations on a subcarrier convey information as to chromaticity lvariations of frequencies below Vone megacycle.

Another object is to provide a receiver for color television signals of the type described in the preceding paragraph in which color Variations of frequency over one megacycle appear on the receiver screen which bear the same ratio to each other as to the color variations of fre quencies below lone megacycle.

Another object is to provide an improved receiver for color television signals of the NTSC recommended standard type.

Still another object is to provide a receiver for color `television signals of the standard NTSC type in which with the three output phases of the local subcarrier source v three signals which respectively comprise areV derived, where G'is a-signal representing the green color variations of frequencies `above one megacycle have the same chromaticity hue and saturation as do color variations in the picture below one megacycle in frequency.

Other objects of my invention will become apparent upon reading the following description taken tion with the "drawings in which:

Figure l is a schematic diagram of a television receiver v embodying the principles of my invention; and

light variations (below one megacycle'in frequency) y the picture; R represents the redlight variations (below one megacycle in frequency), B represents the blue light variations (below one megacycle infrequency), ,andYl isgthefportion of the picture-intensity signal -Y below l niegacycle in frequency. The exponent gammai'y) is a Fig. 2 is a schematic diagram ot' a product amplifier suited for use in the circuit of Fig. 1.

Referring in detail to the drawing, incoming signals of i the NTSC standard type incident onan antennavl are quire detailed description here. The output of the second detector (i.e. Y), passes through suitable filters into three channels; one through a band-pass filter 3 admitting frequencies from A2.5 mc.. to 4 mc.; to a set of Ithree. de-

modulations 5, 6 and 7; a second throughr alowpass(0.

to 1 mc.) lter 4 tothree adding nets 8, 9andv10; and a` third through a high-pass (l mc. to 3.5 mc.) filter 11 tol an adding net 12. An oscillator of subcarrierv(3'.58-mc.)

frequency is synchronized with thesubcarriergenerator;

at the transmitterby sync pulses arriving during the horizontal retrace time and impresses a voltage cophasal with said subcarrier on demodulator 7, a voltage +90 dephed therefrom on demodulator 6 and a voltage +2355 dephased therefrom on demodulator 5.v The exact phase-to be used will dependen thefphases and amplitude of the R, G, and B vectors and on the phase chosen for the reference subcarrier bythe Federal Communication Commission.` As a result of beating the output of` bandpass iilter 3'with the aforesaid subcarrierfrequency voltages the demodulator 5 impresses an output proportional to l (G1 7 Yll) on adding net 8 (where G1 is the signal representing green light intensity variations of frequency under 1 megacycle in the picture and Y1 is the part of Yf varying at frequencies Yunder one megacycle). This it will be noted is the same quantity .derived by the Electronics article system. Demodulator 6 impresses an output proportional to 1 (Raar.)

onadding net 9 (where R1 is the signal representing red proportional to 1 (aan) on adding net (where B1 is the signal representing the blue light intensity variations of frequency under, one megacycle in the picture). Demodulators 5, 6 and 7 thus act in my system just as do demodulators inthe Adding net ySthen adds quantity l (Gn-rf.)

to the output Yl of low pass filter 4 and produces an out- Electronics article.

put

l KQG 7 1 Adding network 9 similarly adds quantity to Yl to produce an output l KSRI Y and adding net 10 adds quantity 1 (Bn-Y1.)

ture 3.58 mc. reference inputs, and to matrix these two signals with Y1 to obtain the three low denition (0 to l me.) color signals.

The output Y'h of high-pass lter 11 is added in an adding network 12 to the output of a voltage source 13 of fixed magnitude and carrier frequency to produce an output proportional to (Y-i-Kl). The latter output is impressed, together .with the output..

from adding net 8, on the input of a product amplifier 14 which impressed on-the,green-emission control electrode light intensity variations at frequency under one megacycle in the picture), and demodulator 7 impresses an otuput of a kinescope system 15 on loutput which is proportional to the product of the quantities which are impressed on its input terminals. A number of different types of product amplifiers are known in the radio art; Figi-2 shows one of these.

The output 1 net 12 are impressed on the input of a second product amplifier 16 to produce an output 12 are impressed on the input of a third product amplilier `17 to produce an output The outputs of product amplifiers 14, 16 and 17 are -respectively impressed on the green-emission, red-emission and blue-emission control electrodes of color-kinescope system 15 thereby producing color images of green-light intensity LG=G1(1{-Yh)l, red-light intensity and blue-light intensity LB=B1(1+Y'h)1-. In order that the relatively simple product amplifier of Fig. 2 may be used K1 should be greater than any of G1, R1 and B1.

It will be noted that, whether intensity variations of frequencies above one megacycle are present or not, (i.e. whether Yh is zero or not), the light intensities LG, LR and LB always bear the same ratios to each other as do the color information signals G1, R1 and B1.

Fig. 2 shows a suitable form for the three product amplifiers 14, 16 and 17 of Fig. 1. Thus the output K1[Yh{-l] from addingnet 12 is impressed across a resistor 21 which has one end grounded and the other end connected to the mid-taps of resistors 22, 23, 24 whose end terminals are connected respectively to the controlelectrode circuits of the green, red and blue phosphor scanning beams in the kinescope system 15. 'I'he output -of adding-net 8 is connected. through two channels 25,

26 embodying similarly poled non-linear resistors 27,

28 (which may for instance be germanium diodes) to the' end terminals of resistor 22. A resistor 29 having its mid-tap grounded interconnects the channels A25, 26.

A set of channels 31, 32 similar to channels 25 and 26,

are connected to the end terminals of resistor 23 and are j oined b y a resistor 33 having its mid-point grounded and its ends impressed with the output v of adding-net 9; and similar channels 34, 35 and resisto 36 connect the output across the ends of resistor 24.

I claim as my invention:

l. A receiving system for producing a color television image defined by a composite signal comprising a first carrier wave having a first given frequency Value, said carrier wave being amplitude modulated by a first intelligence signal indicative of the brightness detail of the elements of said image and having a first frequency spectrum extending to a given maximum frequency value, a second carrier wave having a second given frequency value and a second frequency spectrum arranged adjacent to said maxi-mum frequency value, said second carrier wave having amplitude and phase variations establishing with said first intelligence signal the chromaticity of the elements of said image, said receiving system comprising a first transmission path for amplifying the said composite signal, first detecting means coupled to said first transmission path for producing first and second output signals, said first output signal having variations determined by said first intelligence and indicative of brightness variations of said image, and said second output signal being in the form of a modulated subcarrier Wave having a subcarrier .frequency equal to the difference between said first and second frequency values and defining with said first output signal the chromaticity of said image elements, a low pass filter coupled to said detecting means and adapted to transmit a first component Y1 of said first output signal selectively with respect to a second component Y'h, said first component Yl being indicative of brightness variations of said image occurring at frequencise below one megacycle, said second component Y'h being indicative of brightness variations occurring at frequencies above one megacycle, a high pass filter coupled to said detecting means and adapted to transmit said second component Yh selectively with respect to said first component Y'1, a band pass filter coupled to said detecting means and having a band pass characteristic centered about said subcarrier frequency to transmit said second output signal selectively with respect to components of said first output signal, color signal demodulator means coupled to said band pass filter and responsive to said subcarrier wave to produce first, second and third color difference signals respectively proportional to wherein G1, R1 and B1 are respectively indicative of green, red and blue color intensity fluctuations of said image occurring at frequencies below one megacycle and ly is the power of the control voltage of an electron beam bombarding a luminescent screen to which brightness of said screen is proportional; first, second and third sum producers each having rst and second inputs and an output with said first inputs being coupled in common to said low pass filter and said second inputs being separately coupled to said demodulator means for respectively utilizing said first, second and third color difference signals and said first component Yl to respectively produce low frequency color intensity signals l 1 l G17, R1'y 31nd B17 by adding said first component Y1 to each of said color difference signals, a fourth sum producer coupled to said high pass filter for adding a constant voltage to said second component Yh to producea high frequency image brightness signal K1(Yfh|-l); first, second and third signal multiplying circuits having first inputs coupled in v common to said fourth sum producer and each having second inputs coupled respectively to said first, second andv third sum producers for respectively multiplying said low frequency color intensity signals 'ing said. composite color signals to individually control said electron beams.

r 2. A receiving system for producing a color television image defined by a composite signal comprising a first carrier wave having a first given frequency value, said carrier wave being amplitude modulated by a first intelligence signal Y indicative of the brightness detail of the elements of said image and having a first frequency spectrum extending to a given maximum frequency value, a second carrier Wave having a second given frequency value and a second frequency spectrum arranged adjacent to said maximum frequency value, said second carrier wave having amplitude and phase variations establishing with said first intelligence signal the chromaticity of the elements of said image, said receiving system comprising a first transmission path for applying the said composite signal, first detecting means connected to said first transmission path for producing first and second output'signals, said first output signal having variations determined by said first intelligence and indicative of brightness variations oftsaid image, and said second to said detecting means and adapted to transmit a first component Y'l of said first output signal selectively with respect to a second component Yh, said first component Y1 being indicative of brightness variations of said image occurring at frequencies below one megacycle, said second component Yh being indicative of brightness variations occurring at frequencies above one megacycle, a high pass filter connected to said detecting means and adapted to transmit said second component Y'h selectively with respect to said first component Y1, color'` signal demodulator means connected to said detector and responsive to said subcarrier wave to produce first, second and third color difference signals respectively proportional to 1 1 1 (61117'- Yi), (R17 Y'1) Mld (B17- Y'i) wherein G1, R1 and B1 are respectively indicative of green, red and blue color intensity iiuctuations of said image occurring at frequencies below one megacycle and 'y is the power of the control voltage of an electron'beam bombarding a luminescent screen to which brightness of said screen is proportional; first, second and third sum producers each having first and second inputs and an output with said first inputs being connected in common to said low pass filter and said second inputs being separately connected to said demodulator means for respectively utilizing said first, second and third color difference vsignals and said first component Y 1 torespectively produce low frequencycolor intensity signals l 1 l G17, R17 and .B1Y by adding said rst component Y', to each of said color diiference signals; a fourth sum producer connected to said high pass filter vfor adding a constant voltage to said second component Yh to produce a high frequency image brightness signal K1(Yh{l); rst, second and third signal multiplying circuits having `first inputs con` nected in common to said fourth sum prdoucer and each having second inputs connected respectively to said rst, second and third sum producers for respectively multiplying said low frequency color intensity signals l 1 l G1'y, R17 21nd B1.Y by said high frequency brightness signal K1(Yh11) to respectively produce rst, second and third composite color signals in which variations at frequencies abovev one mcgacycle have the same ratio to each other as variations below one megacycle; color image Yreproducing means including first, second and third electron beams for respectively bombarding red, green and blue luminescent materials, and means for respectively applying said composite color signals toindividually control said electron beams.

References Cited in the le of this patent UNITED STATES PATENTS 2,680,147 Rhodes June 1, 1954 2,734,310 Schroeder Apr. 24, 1956 2,745,900 Parker May 15, 1956 2,754,356 Espenlaub July 10-, 1956 2,779,818 Adler Jan. 29, 1957 OTHER REFERENCES Principles of NTSC Compatible Color Television, Electronics, February 1952, Hirsch, Bailey and Loughlin, pages 88 to 95.

NTSC Color TV, Dome, Electronics, February 1952, pages 96 and 97.

Two-Color Receiver for RCA Color Television System, November 1949, pages 1 to 15.

Principles of NTSC, Hirsch, Electronics, February 1952.

Introduction to Color Television, Admiral Corp., Feb- 25 ruary 1954, Chicago, Ill. 

